Dorothea Quarry has seen the scene of a number of diving fatalities
Two people have been airlifted to a decompression unit after one of them showed signs of the bends after diving at a quarry in Snowdonia.
The couple, from Manchester, had dived into the lake at Dorothea Quarry in the Nantlle Valley, Gwynedd.
The woman was treated by a paramedic after surfacing rapidly when it was decided both divers should be flown to private hospital on Wirral.
More than 20 people have died at the quarry pool since 1994.
The lake at Dorothea Quarry is up to 300ft (90.9m) deep in places, with a network of flooded tunnels and sheer drops.
It is used as a training location by some amateur divers from across the UK, although there are warnings about its dangers.
The divers were flown to hospital by the RAF Sea King helicopter based at Valley on Anglesey.